Abstract
Most domestic wastewater can be effectively treated for secondary uses by engineered biological systems. These systems rely on microbial activity to reduce nitrogen (N) content of the reclaimed water. Such systems often employ a tidal-flow process to minimize space requirements for the coupling of aerobic and anaerobic metabolic processes. In this study, laboratory-scale tidal-flow treatment systems were studied to determine how the frequency and duration of tidal cycling may impact reactor performance. Fluorescent in situ hybridization and epifluorescence microscopy were used to enumerate the key functional groups of bacteria responsible for nitrification and anaerobic ammonium oxidation (anammox), and N-removal efficiency was calculated via a mass-balance approach. When water was cycled (i.e., reactors were filled and drained) at high frequencies (16–24 cycles day−1), nitrate accumulated in the columns—presumably due to inadequate periods of anoxia that limited denitrification. At lower frequencies, such as 4 cycles day−1, nearly complete N removal was achieved (80–90%). These fill-and-drain systems enriched heavily for nitrifiers, with relatively few anammox-capable organisms. The microbial community produced was robust, surviving well through short (up to 3 h) anaerobic periods and frequent system-wide perturbation.
Highlights
Despite vast quantities of water on earth, a mere 3% is suitable for human consumption [1].As populations grow, the need for potable water will continue to increase, and water re-use is key to meeting this demand
When the high-N reactor was operated at 24 cycles day−1 (Figure 2a), a significant increase in abundance was observed with depth for total bacteria, ammonium oxidizing bacteria (AOB), and nitrite oxidizing bacteria (NOB) (Table 1); a similar change in AOB and NOB was evident in the low-N reactor (Figure 2b)
N-oxidizing bacteria in the community; AOB and NOB collectively were ~30% of the total bacterial abundance while Anammox bacteria (AXB) was always less than 2%
Summary
Despite vast quantities of water on earth, a mere 3% is suitable for human consumption [1].As populations grow, the need for potable water will continue to increase, and water re-use is key to meeting this demand. One promising approach to address the growing water crisis is to develop more efficient and affordable on-site means of treating water for secondary uses in hopes of reducing unnecessary demand on the potable water supply. A key consideration when treating water for secondary uses is removal of reactive nitrogen (N). Though there are physiochemical treatments for removing N, biological systems that rely on microbial processes are more efficient, reliable, and effective [4,5,6]. These systems depend on the synergistic relationships among several different functional groups of microorganisms to convert reactive N to inert N2 gas
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